open System.IO

let streamWriter1 = File.CreateText("test1.txt")
let count = 10000000
let buffer = Array.init count (fun index -> byte (index % 256))

printfn "Writing to file test1.txt."
let asyncResult = streamWriter1.BaseStream.BeginWrite(buffer, 0, count, null, null)

// Read a file, but use the waitHandle to wait for the write operation
// to be completed before reading.
let readFile filename waitHandle count =
    async {
        let! returnValue = Async.AwaitWaitHandle(waitHandle)
        printfn "Reading from file test1.txt."
        // Close the file.
        streamWriter1.Close()
        // Now open the same file for reading.
        let streamReader1 = File.OpenText(filename)
        let! newBuffer = streamReader1.BaseStream.AsyncRead(count)
        return newBuffer
    }

let bufferResult = readFile "test1.txt" asyncResult.AsyncWaitHandle count
                   |> Async.RunSynchronously